The process of manufacturing roofing shingles involves pulling a web though a production line and applying raw materials such as asphalt and granule to the web. The width of the web allows for the production of multiple lanes of shingles simultaneously. Once the raw materials have been applied to the web, the web is sliced, sometimes overlaid to form architectural shingles, and cut to produce individual shingles. The final cutting operation typically occurs at a “chop cutter,” which cuts moving ribbons of shingle stock transversely across their width to form the individual shingles. These individual shingles may leave the chop cutters in rapidly moving streams of individual shingles, which can be configured in pairs that usually are oriented in back-to-back relationship.
In the past, a stream of individual shingles would leave the chop cutters and be transported from the chop cutters by infeed conveyor to a downstream auto-catcher. The function of the auto-catcher is to catch the shingles in the moving stream in such a way that the shingles are stacked in bundles in the auto-catchers. When a predetermined number of individual shingles have been collected into a bundle in the auto-catcher, the bundle is released onto another series of conveyors that transport the bundle to one or more wrappers, which wrap the bundles for shipment.
As shingle production rates progressively increased, traditional auto-catchers became a bottleneck in the shingle production process due, among other things, to the limited capability of the auto-catcher. More specifically, a single auto-catcher was not capable of catching and releasing reliably all the shingles produced at such higher production rates. A solution was to install a second auto-catcher in-line with the first original auto-catcher and a diverter configured to divert each shingle alternately to separate infeed conveyors of the first or the second auto catcher. The diverters allowed the shingles to be fed to both auto-catchers such that each auto-catcher only needed to operate at half the speed of a single auto-catcher.
One common shingle diverter known as an “up-down” or “wig-wag” converter, includes a set of fingers along the path of the moving stream of shingles that can be moved rapidly by a servo motor between a lowered position and a raised position. In the lowered position of the diverter, a shingle of the moving stream passes over the diverter and continues along a first path to the infeed conveyor of a first auto-catcher. In the raised position of the diverter, its fingers define a ramp up which an approaching shingle rides toward a second infeed conveyor that carries the shingle to the second auto-catcher. In some manufacturing plants, shingles may be diverted down to the second infeed conveyor rather than up.
FIG. 1 illustrates a prior art wig-wag diverter in simplified schematic fort to illustrate the just described operation. Here, a wig-wag diverter 19 is positioned near the end of a main infeed conveyor 12 and just upstream of a first path infeed conveyor 13 and a second path infeed conveyor 14. The diverter 19 includes diverter fingers between the conveyor belts that can be rapidly moved by a servo between a lowered position 21 and a raised position 22. As a shingle 17 approaches the diverter 19 when the diverter is in its lowered position 21 the shingle moves over and past the diverter onto the first catcher infeed conveyor 13 as indicated at 16. This conveyor carries the shingle to a first auto-catcher (not shown). Alternately, as a shingle 17 approaches the diverter when the diverter is in its raised position 22, the shingle rides up the ramp defined by the diverter fingers and is directed onto a second catcher infeed conveyor 14. This second conveyor carries the shingle to a second auto-catcher (not shown). The diverter fingers are raised and lowered between successive shingles so that shingles are directed in alternating sequence to the first and to the second auto-catcher.
Typically, shingles leave the chop cutters in end-to-end relationship with no space between individual shingles. In order to create spacing between successive shingles sufficient to allow the diverter fingers to move to their raised position between shingles, the shingles are accelerated as they leave the chop cutter by the belts of the diverter infeed conveyor. For a typical diverter with 7 inch fingers, a chop cutter or production speed of 800 feet per minute (fpm), and shingles that are 39.375 inches long for example, about 15 inches of space is required between successive shingles. This requires that the diverter infeed belts be driven at about 1105 fpm [(15″+39.375″)/39.375″=1.38 percent speed increase. 1.38×800 fpm=1105 fpm.] As production speeds increase even higher, the shingles must be accelerated to even higher speeds in a shorted period of time before encountering the diverter to increase the spacing between shingles. This, in turn, can have an increasingly adverse impact on other areas of the machine for at least the following primary reasons.
(1) Slip—as a shingle is accelerated by the diverter infeed conveyor in a shorter period of time between the cutter and the diverter, the amount of slip between the shingle and the conveyor belts increases and inconsistency in shingle spacing results. This is due, among other reasons, to factors such as the distance available to accelerate each shingle and the limited friction between the belts and the shingles. There is therefore a practical limit to the speed to which the shingles can be accelerated in a controlled manner in a given distance or time. This, in turn, limits cutter speed and thus production speed.
(2) Deceleration—while the shingles must be accelerated by the diverter infeed conveyor to create spacing for diverting, they likewise must be decelerated by the catcher infeed conveyors before moving into the auto-catchers. This is because it is nearly impossible to catch shingles traveling at extremely high speeds. As a shingle moves into the auto-catcher it must come to a complete stop. Shingle are not rigid enough to enter the auto-catcher at a high rate of speed and stop instantaneously without deforming. The requirement to decelerate the shingles after they are accelerated through the diverter gives rise to the same slip and inconsistency issues encountered during acceleration, and therefor represents a limitation processing speed. These limiting issues are usually most prominent for the most upstream auto-catcher because the shingles must be decelerated in a shorter distance for this auto catcher.
(3) Diverting a shingle from a horizontal path to an upwardly angled path at higher speeds can cause the shingle to “fly.” In other words, the shingle can move so fast that the diverter launches the shingle into air rather than moving it reliably onto a conveyor. The faster the shingles are traveling when they encounter the diverter the less control one has over this phenomenon. This again is a limiting factor that can limit production rates.
The above problems cannot be solved simply by reducing spacing between individual shingles, and thereby reducing required acceleration and deceleration rates. This is because for a traditional wig-wag diverter such as that shown in FIG. 1, the length of the diverter fingers limits the required minimum distance between individual shingles. More specifically, a leading shingle must travel completely past the diverter before the divert fingers can be moved from a lowered position to a raised position. If the fingers begin to lift before the tail of a leading shingle clears the diverter, the fingers will flip the tail of the shingle up and cause a jam. Once the leading shingle passes the diverter, the diverter fingers must cycle completely to their raised positions before the leading edge of the next trailing shingle makes contact with the diverter. If the leading edge of the next shingle is on the diverter while it is still moving to its raised position, the shingle will be flipped or launched into the air by the rapidly moving diverter fingers and likely cause a jam. These constraints coupled with the cycle time of the programmable logic controller (PLC), distance moved by the shingles per PLC cycle, photo eye delays, speeds at which information can be passed to the input card of the controller, and the time it takes the servo motor to move the diverter fingers from their lowered position to their raised position dictates the required minimum spacing between shingles. For a machine with traditional 7″ long diverter fingers and shingles moving at 1105 fpm, this minimum spacing is about 15″. Reducing the spacing below this minimum is not possible for a given machine with a traditional wig-wag diverter.
A method and apparatus re therefore needed for significantly reducing the required minimum spacing between shingles as they move through a diverter in order to reduce acceleration and deceleration rates of the shingles for a given machine production speed. Alternatively, such method and apparatus should allow production speeds to be increased while not taxing the limitations of the diverter and auto-catchers. It is to the provision of such a method and apparatus that the present disclosure is primarily directed.